C0G capacitors have very low temperature drift Temperature Coefficient of Capacitance (TCC) (≦+/−30 ppm/° C.). Typically, the primary components of the ceramic include magnesium titanate or barium neodymium titanate.
The use of base metal electrodes such as Ni, Cu, and 80 Ni:20 Cu for capacitors offer significant material cost advantages over noble metals or precious metal electrodes such as Pt, Pd, Au, Ag and combinations thereof. Ni and Cu are conductive, comparatively inexpensive metals which, in pure form, are not facilely oxidized. Both can be deposited as electrodes using screen printing processes on the same equipment conventionally used for depositing noble metals. Ni has a higher melting point (Ni mp 1450° C.; Cu mp 1083° C.—Weast Handbook of Chemistry & Physics, 46th edition) and is preferred for multi-layered ceramic capacitors (MLCC) fired at higher temperatures.
While the ceramic dielectrics of this invention may be used with precious metals to obtain C0G MLCC capacitors (which may be fired in oxidative environments), BME capacitors are preferred.
Numerous compositions have been disclosed for non-reducing type dielectric ceramic compositions including U.S. Pat. Nos. 5,204,301; 6,118,648; 6,295,196; 6,329,311; 6,387,835; 6,396,681; 6,327,311; 6,525,628; 6,572,793; 6,645,897; 6,656,863; 6,858,554 and 7,172,985 as well as published patent application numbers US 2005/0111163; US 2003/0186802 and US 2004/0220043. These disclosures are directed to various combinations of Ca, Sr, Zr, Ti and Ba oxides with or without limited amounts of dopant oxides or alkaline, alkaline earth and rare earth metals wherein individual precursors are fired to form a ceramic matrix. These ceramics, though beneficial, are still inferior with regards to overall capacitor performance. There has been an ongoing effort in the art to provide a capacitor with improved properties and, specifically, to ceramics which can provide an improved capacitor.